Osotogari and hizaguruma go together like peas and carrots. Actually better - nobody around here actually eats peas and carrots together, but I know from experience that these two techniques partner so well that learning one of them well impoves your performance of the other one. The reason that they go so well together is that they are dynamic opposites that occur from the same position. One is a forward throw and one a backward throw. One is (usually) an otoshi motion, the other a guruma. One is an attack on the near leg, the other attacks the far leg. One attacks an offbalance parallel to the opponent's stance line and the other attacks his perpendicular.
So it's just incredibly hard to avoid taking one of these two falls if you let the other guy get anywhere close to that position.